The development of fuel cells is intensifying, since it is said that fuel cells are a power generation system having good energy utilization efficiency. Among fuel cells, polymer electrolyte fuel cells are especially drawing attention due to their high power density and ease of handling.
For a fuel cell, which generates power through an electrochemical reaction between hydrogen and oxygen, it is essential to establish hydrogen supply means. One method for doing this is to produce hydrogen by reforming a raw material for hydrogen production such as a hydrocarbon fuel. From the viewpoint that supply systems of hydrocarbon fuels are already socially established, this method is more advantageous than methods in which pure hydrogen is used.
Examples of hydrocarbon fuels include city gas, LPG, gasoline, kerosene, gas oil and the like. In order to use these raw materials for hydrogen production in fuel cells, hydrogen must be produced from the hydrocarbon. For this purpose, a hydrogen production apparatus equipped with at least a reformer is used.
In a hydrogen production apparatus, for example, a hydrocarbon is reacted with water in a reformer to decompose into mainly carbon monoxide and hydrogen. Then, a large portion of the carbon monoxide is reacted with water in a shift reactor to convert into hydrogen and carbon dioxide. Finally, the remaining small amount of carbon monoxide is reacted with oxygen in a preferential oxidation reactor to turn into carbon dioxide. Further, since sulfur may be a poisoning substance for reforming catalyst or the like, in many cases a desulfurizer is provided for removing the sulfur contained in the hydrocarbon fuel.
In such a hydrogen production apparatus, it is a known practice to cool an outlet gas of the shift reaction part using water or air (ambient air) in order to bring the temperature of the preferential oxidation reaction part to a proper temperature or in order to remove the water content in the gas to be supplied to the preferential oxidation reaction part (Patent Documents 1 to 4).    Patent Document 1: JP2002-284505A    Patent Document 2: JP2003-12302A    Patent Document 3: JP2003-17109A    Patent Document 4: JP2004-296266A